We have successfully made free whole muscle autografts of extensor digitorum longus muscles of cats. The muscles have either been autografted back into the same site, orthotopic autografts, or autografted into the contralateral site, heterotopic autografts. The autografts were made either with denervation of the muscle 3-4 weeks prior to the autografting procedure (pre-denervated autografts) or with denervation at the time of autografting (normal autografts). No significant differences were found between the orthotopic and heterotopic and autografts or between the pre-denervated and normal autografts. The autografts underwent a period of degeneration followed by regeneration of skeletal muscle fibers. The restoration of control structure and function in the autografts was evaluated by histological, electron microscopical, histochemical, biochemical, electro-myographical, and contractile properties. An objective was to assess the time required for the autografts to attain stability. This was complicated by the variability amongst the different variables. The fiber cross-sectional area reached control values by 120 days and then increased a further 30%, whereas succinate oxidase activity, capillarity, percentage slow twitch fibers, percentage fatigue resistant fibers did not reach control values by 400 days. Some autografts attained some aspects of structure and function that were not significantly different from controls. We are analyzing the factors that contribute to a restoration of control values. We conclude that pre-denervation is not necessary for a successful autograft and that sufficient function is restored for autografted muscles to be clinically useful in specific cases.